Remember when we told you to brace yourself because the death of unlimited wireless data in the United States is imminent? Well, the beginning of the end is finally upon us: Sprint, one of unlimited mobile data’s last and biggest and last defenders, has begun to throttle some wireless subscribers with unlimited data plans. FierceWireless on Thursday reported that Sprint is “slamming the brakes” on unlimited high-speed data for around 5% of its wireless customers in congested areas. According to the report, postpaid Sprint customers and prepaid subscribers on Virgin Mobile or Boost Mobile are being throttled. “[Throttling] will enable us to provide more customers with a high quality data experience during heavy usage times,” Sprint said in a statement to